This invention relates to flame-retardant polycarbonate resin compositions. More particularly, it relates to flame-retardant polycarbonate resin compositions improved in flame retardance without sacrificing the inherent outstanding properties of the polycarbonate resin, such as impact resistance and other mechanical properties, flow properties, and outward appearance of molded parts, and which contain neither a halogen type flame retardant containing chlorine or bromine compound or a phosphorus type flame retardant.
Polycarbonate resins, a class of engineering plastics with excellent transparency, impact strength, heat resistance, and electrical properties, are used extensively in electrical, electronic, office automation, and many other applications.
In the electrical-electronic and OA fields there are many components, such as personal computer housings, that are required to possess high flame retardance (conforming to Underwriters"" Laboratories (UL) 94V ratings) and great impact resistance. Polycarbonate resins are self-extinguishing, highly flame-retardant plastics themselves. Still, in electrical-electronic and OA applications where safety is the primary consideration, they are required to have even greater flame retardance, high enough to meet the requirements of UL94V-0 and 94V-1.
A commonly used method to improve the flame retardance of the polycarbonate resin has been to mix it with a large proportion of an oligomer or polymer of a carbonate derivative of brominated bisphenol A.
Problems Encountered
The large addition of an oligomer or polymer of a carbonate derivative of brominated bisphenol A improves the flame retardance of the polycarbonate resin. However, it reduces the impact resistance of the resin and thereby poses a problem of frequent cracking of articles molded from the resin.
On the other hand, mixing the resin with a large amount of a halogen type compound that contains bromine can evolve a gaseous product containing the particular halogen upon combustion. Thus from environmental considerations there is a demand for the use of a flame retardant free from chlorine, bromine or the like.
Meanwhile, many attempts have thus far been made to utilize silicone compounds as flame retardants. The compounds have high heat resistance, produce negligible noxious gas upon combustion, and are remarkably safe in use.
The silicone compound as a flame retardant s a polymer that results from the polymerization of at least any of the following four siloxane units (unit M, unit D, unit T, and unit Q). 
where R represents an organic group. 
where R represents an organic group. 
where R represents an organic group. 
Of these units, unit T and/or unit Q, when contained in the compound, forms a branched structure.
In order to utilize silicone compounds as flame retardants, various silicone compounds having organic groups have hitherto been tried, as taught in Japanese Patent Application Public Disclosure (Kokai) No. 1-318069, Japanese Patent Application Publication (Kokoku) No. 62-60421, etc.
However, very few of those compounds can achieve an appreciable flame-retarding effect when added singly. Even one found relatively effective must be added in a large quantity if it is to meet the strict standards for electrical-electronic appliances. The large addition is not practicable because it unfavorably affects the molding, kneading, and other needed properties of the resulting plastics, and also because it adds to the cost.
Methods of combining a silicone compound with a metal salt have been reported as attempts to enhance the flame-retarding effect of a silicone compound while reducing the amount to be added. They include the combined use of polydimethyl silicone, a metal hydroxide, and a zinc compound (Japanese Patent Application Public Disclosure (Kokai) No. 2-150436) polydimethyl silicone and a Group IIa metal salt of an organic acid (Japanese Patent Application Public Disclosure (Kokai) No. 56-100853); and silicone resin, especially one represented by units M and Q, silicone oil, and a Groups IIa metal salt of an organic acid (Japanese Patent Application Publication (Kokoku) No. 3-48947). Fundamental problems common to those methods are inadequate flame-retarding effect and difficulty in substantially reducing the amount to be added.
A further combination of an organopolysiloxane having an epoxy group (xcex3-glycidoxypropyl group) and phenyl group and/or vinyl group and an alkali metal salt and alkaline earth metal salt of an organic sulfonic acid (Japanese Patent Application Public Disclosure (Kokai) No. 8-176425) has been reported. Since this silicone compound contains highly reactive epoxy and vinyl groups, the silicone compound can react with itself to form high molecular weight gels when mixed with the polycarbonate resin, because of high temperature, hampering thorough mixing and increasing the viscosity of the mixture. This presents problems of undesirable polycarbonate resin moldability, especially delamination, sinking, and/or unevenness of molded part surface. Moreover, the gelation does not allow the silicone compound to be thoroughly dispersed in the polycarbonate resin. This, in turn, causes problems of difficulty in attaining a noticeable flame-retarding effect and of declined strength properties such as impact strength of the molded articles.
The present inventors have intensively searched for a solution of the afore-described problems of the prior art. They have now found, as a result, that the combined use of a specific silicone compound and a metal salt of an aromatic sulfur compound or a metal salt of a perfluoroalkanesulfonic acid as a flame retardant to be mixed with a polycarbonate resin and the additional use of a fiber-forming fluoropolymer provide flame-retardant polycarbonate resin compositions possessing high flame retardance without a sacrifice of their impact resistance and molding properties. The finding has led to the perfection of the present invention.
The flame-retardant polycarbonate resin compositions according to the invention, free from a bromine type or other halogen type flame retardant, have no danger at the time of combustion of evolving gases containing the halogen that results from the halogen type flame retardant, and thereby exhibit outstanding performance from the viewpoint of environmental protection.
In brief, the invention concerns a flame-retardant polycarbonate resin composition characterized by mixing a polycarbonate resin (A) with a silicone compound (B) whose backbone structure is branched and which has aromatic groups in the organic groups it contains, and a metal salt of an aromatic sulfur compound (C) or a metal salt of a perfluoroalkanesulfonic acid (D). It also concerns a flame-retardant polycarbonate resin composition characterized by the addition of a fiber-forming fluoropolymer (E). The flame-retardant polycarbonate resin compositions according to the invention will now be described in detail.
The polycarbonate resin (A) to be used in this invention is any of the polymers obtained either by the phosgene process in which one of varied dihydroxydiaryl compound is reacted with phosgene or by the ester exchange process in which a dihydroxydiaryl compound is reacted with a carbonic ester such as diphenyl carbonate. Typical of them is a polycarbonate resin produced from 2,2-bis(4-hydroxyphenyl)propane (bisphenol A).
Examples of the dihydroxydiaryl compounds, besides bisphenol A, are: bis(hydroxyaryl)alkanes, such as bis(4-hydroxyphenyl)methane, 1,1-bis(4-hydroxyphenyl)ethane, 2,2-bis(4-hydroxyphenyl)butane, 2,2-bis(4-hydroxyphenyl)octane, bis(4-hydroxyphenyl)phenylmethane, 2,2-bis(4-hydroxyphenyl-3-methylphenyl)propane, 1,1-bis(4-hydroxy-3-tert.butylphenyl)propene, 2,2-bis(4-hydroxy-3-bromophenyl)propane, 2,2-bis(4-hydroxy-3,5-dibromophenyl)propane, and 2,2-bis(4-hydroxy-3,5-dichlorophenyl)propane; bis(hydroxyaryl)cycloalkanes, such as 1,1-bis(4-hydroxyphenyl)cyclopentane and 1,1-bis(4-hydroxyphenyl)cyclohexane; dihydroxydiaryl ethers, such as 4,4xe2x80x2-dihydroxydiphenyl ether and 4,4xe2x80x2-dihydroxy-3,3xe2x80x2-dimethyldiphenyl ether; dihydroxydiaryl sulfides, such as 4,4xe2x80x2-dihydroxydiphenyl sulfide; dihydroxyaryl sulfoxides, such as 4,4xe2x80x2-hydrodiphenyl sulfoxide and 4,4xe2x80x2-dihydroxy-3,3xe2x80x2-dimethyldiphenyl sulfoxide; and dihydroxydiaryl sulfones, such as 4,4xe2x80x2-dihydroxydiphenyl sulfone and 4,4xe2x80x2-dihydroxy-3,3xe2x80x2-dimethyldiphenyl sulfone.
These are used singly or as a mixture of two or more. It is preferred that these compounds are not halogenated, so that they do not release halogen-containing gases into the atmosphere during combustion. Such a compound or compounds may be used in mixture with piperazine, dipiperidylhydroquinone, resorcin, 4,4xe2x80x2-dihydroxydiphenyl, etc.
The dihydroxyaryl compound or compounds may be used in combination with a trivalent or more polyvalent phenol compound as follows.
Tri- or more polyvalent phenols include phloroglucin, 4,6-dimethyl-2,4,6-tri(4-hydroxyphenyl)heptene, 2,4,6-dimethyl-2,4,6-tri(4-hydroxyphenyl)heptane, 1,3,5-tri(4-hydroxyphenyl)benzole, 1,1,1-tri(4-hydroxyphenyl)ethane, and 2,2-bis[4,4-(4,4xe2x80x2-dihydroxydiphenyl)cyclohexyl]propane.
The viscosity-average molecular weight of a polycarbonate resin (A) is usually between about 10,000 and about 100,000, preferably between about 15,000 and about 35,000. In preparing such a polycarbonate resin, it is possible to use a molecular weight modifier, catalyst, and/or other additive according to the necessity.
The silicone compound (B) to be used in the invention is one whose backbone structure is branched and which contains aromatic groups as organic groups (R1, R2 and R3), as represented by the general formula (1). 
where R1, R2, and R3 represent organic groups in the main chain, X represents an end functional group, and n, m and I represent the number of each unit.
The compound is characterized by having unit T and/or unit Q as the branching unit. It is desirable that the amount of such units contained in the compound accounts for at least about 20 mol % of the total siloxane unit content. If it is less than about 20 mol %, the resulting silicone compound (B) has inadequately low heat resistance and reduced flame-retarding effect and shows such low viscosity that it can have adverse effects upon miscibility with a polycarbonate resin (A) and upon the moldability of the resulting composition. A more desirable range is between about 30 and about 95 mol %. A unit proportion in excess of about 30 mol % further increases the heat resistance of the silicone compound (B) and substantially enhances the flame retardance of the polycarbonate resin that contains the compound. Beyond about 95 mol %, however, the units decrease the degree of freedom of the silicone""s principal chain, frequently hampering the condensation of the aromatic ring during combustion and rendering it difficult to exhibit remarkable flame retardance.
It is also advisable that the silicone compound (B) should contain organic groups of which aromatic groups account for at least about 20 mol %. Below this limit condensation among the aromatic rings tends to occur scarcely during combustion, thus reducing the flame-retarding effect. A preferred range is between about 40 and about 95 mol %. Over about 40 mol % the aromatic groups condense more effectively during combustion while, at the same time, the dispersibility of the silicone compound (B) in the polycarbonate resin (A) is substantially enhanced, and a very high flame-retarding effect is achieved. Beyond about 95 mol %, however, steric hindrance among the aromatic groups tends to obstruct their condensation, sometimes making it difficult to attain a noticeable flame-retarding effect.
The aromatic groups to be contained are phenyl, biphenyl, naphthalene, or their derivatives. The phenyl group is preferred from the view point of industrial hygiene of the silicone compound (B). Of the organic groups in the silicone compound (B), the organic group other than the aromatic group is preferably methyl group. It is also desirable that the end group is one or a mixture of two to four different groups selected from the class consisting of methyl group, phenyl group, hydroxyl group, and alkoxy groups (especially methoxy group). These end groups, with low reactivity, rarely cause gelation (crosslinking) of the silicone compound (B) during the mixing of the compound with the polycarbonate resin (A). Consequently, the silicone compound (B) can be uniformly dispersed in the polycarbonate resin (A), whereby a better flame-retarding effect is achieved and enhanced moldability is attained. Particularly desirable is methyl group, which, with exceptionally low reactivity, brings extremely desirable dispersibility and a further improvement in flame retardance.
The (weight) average molecular weight of the silicone compound (B) desirably ranges from about 5,000 to about 500,000. If it is less than about 5,000, the heat resistance of the silicone compound itself is insufficient, with a reduced flame-retarding effect. In addition, the melt viscosity is so low that the silicone compound can bleed to the surface of a molded part of the polycarbonate resin (A) at the time of molding, thus often affecting the moldability unfavorably. Conversely if it is more than about 500,000, the melt viscosity increases excessively to hinder the uniform dispersion of the compound in the polycarbonate resin (A). This sometimes decreases in the flame-retarding effect or moldability. A more desirable range is from about 10,000 to about 270,000. In this range the melt viscosity of the silicone compound (B) is optimum, enabling the compound to be most uniformly dispersed in the polycarbonate resin (A) with no excessive bleeding to the surface, thus realizing even higher flame retardance and moldability.
The amount of silicone compound (B) to be used desirably ranges from about 0.01 to about 8 parts by weight per 100 parts by weight of the polycarbonate resin (A). When the amount is less than about 0.01 part by weight, the flame-retarding effect is sometimes insufficient. When it is more than about 8 parts by weight, delamination can mar the appearance of the molded articles. A more desirable range is from about 0.1 to about 5 parts by weight, and even more desirable range is from about 0.5 to about 2 parts by weight. In the last-mentioned range, a better balance is attained between the flame retardance and moldability and between them and impact strength.
The metal salt of an aromatic sulfur compound (C) to be used in the present invention is either a metal salt of an aromatic sulfonamide of the general formula (2) or (3) below or a metal salt of an aromatic sulfonic acid of the general formula (4) below. 
(In the general formula (2) Ar is a phenyl or substituted phenyl group and M is a metal cation.) 
(In the general formula (3) Ar is phenyl or substituted phenyl group, Rxe2x80x2 is an organic group that may contain a sulfonyl or carbonyl group, and M is a metal cation, with the proviso that Ar may be a phenylene to link with Rxe2x80x2.) 
(In the general formula (4) Rxe2x80x3 and Rxe2x80x2xe2x80x3 are the same or different and represent aliphatic groups containing 1 to 6 carbon atoms, phenyl, biphenylyl or substituted phenyl or biphenylyl groups, and A represents an SO3M group, in which M is a metal cation.)
Desirable examples of metal salts of aromatic sulfonamides are metal salts of saccharin, metal salts of N-(p-tolylsulfonyl)-p-toluenesulfoimide, metal salts of N-(Nxe2x80x2-benzylaminocarbonyl)sulfanylimide, and metal salts of N-(phenylcarboxyl)-sulfanylimide. Metal salts of aromatic sulfonic acids are, for example, metal salts of diphenylsulfone-3-sulfonic acid, diphenylsulfone-3,3xe2x80x2-disulfonic acid, and diphenylsulfone-3,4xe2x80x2-disulfonic acid. They may be used singly or in combination.
Suitable metals are Group I metals (alkali metals) such as sodium and potassium, Group II metals (alkaline earth metals), copper, aluminum, etc., especially alkali metals.
Preferred above these are potassium salts, such as potassium salt of N-(p-tolylsulfonyl)-p-toluenesulfoimide, potassium salt of N-(Nxe2x80x2-benzylaminocarbonyl)sulfanylimide, and potassium salt of diphenylsulfone-3-sulfonic acid. More preferred are potassium salt of N-(p-tolylsulfonyl)-p-toluenesulfoimide and potassium salt of N-(Nxe2x80x2-benzylaminocarbonyl)sulfanylimide.
The amount of a metal salt of an aromatic sulfur compound (C) to be used desirably ranges from about 0.03 to about 5 parts by weight per 100 parts by weight of a polycarbonate resin (A). When the amount is less than about 0.03 part by weight, it is sometimes hard to attain a noticeable flame-retarding effect, with adverse effects upon the moldability and impact strength. A preferred range is between about 0.05 and about 2 parts by weight, and a more preferred range is between about 0.06 and about 0.4 part by weight. In this range, above all, flame retardance, moldability, and impact strength are better balanced.
The metal salt of a perfluoroalkanesulfonic acid (D) to be used in this invention is a metal salt of formula (5) below: 
in which M is a metal cation and n is an integer of 1 to 8.
The metal salt of a perfluoroalkanesulfonic acid (D) includes a metal salt of a perfluoromethanesulfonic acid, a metal salt of a perfluoroethanesulfonic acid, a metal salt of a perfluoropropanesulfonic acid, a metal salt of a perfluorobutanesulfonic acid, a metal salt of a perfluoropentanesulfonic acid, a metal salt of a perfluorohexanesulfonic acid, a metal salt of a perfluoroheptanesulfonic acid, a metal salt of a perfluorooctanesulfonic acid and the like or a mixture thereof. The metal salt of a perfluoroalkanesulfonic acid may be used in combination with the aromatic sulfur compound (C) described above.
The metal used in the metal salt of a perfluoroalkanesulfonic acid (D) includes Group I metals (alkali metals) such as sodium and potassium, Group II metals (alkaline earth metals), copper and aluminum. The alkali metal is preferred.
Preferred metal salt of a perfluoroalkanesulfonic acid (D) is a potassium salt of a perfluorobutanesulfonic acid.
The amount of a metal salt of a perfluoroalkanesulfonic acid (D) is about 0.01 to about 5 parts by weight based on 100 parts by weight of polycarbonate resin (A). If the amount is smaller than about 0.01 part by weight, its flame retardance is sometimes insufficient, whereas an amount beyond about 5 parts by weight may result in a poor thermal stability on injection molding, which may badly influence the moldability or the impact strength. The amount is preferably about 0.02 to about 2 parts by weight, and more preferably about 0.03 to about 0.2 parts by weight. The latter range particularly brings a good balance among flame retardance, moldability and impact strength.
The fiber-forming fluoropolymer (E) to be used in this invention desirably is one which forms a fiber (fibril type structure) structure in a polycarbonate resin (A). Useful are polytetrafluoroethylenes, tetrafluoroethylene copolymers (e.g., tetrafluoroethylene/hexafluoropropylene copolymer), partially fluorinated polymers as taught by U.S. Pat. No. 4,379,910, and polycarbonates produced from fluorinated diphenol. When such a polymer is used together with a combination of a silicone compound (B) and a metal salt of an aromatic sulfur compound (C), or a combination of a silicone compound (B) and a metal salt of a perfluoroalkanesulfonic acid (D) according to the invention, it proves effective not only in preventing dripping but in specifically shortening combustion time.
The amount of a fiber-forming fluoropolymer (E) to be used is in the range from about 0.05 to about 5 parts by weight per 100 parts by weight of a polyearbonate resin (A). If the amount is smaller than about 0.05 part by weight, its dripping-preventive effect during combustion is sometimes insufficient, whereas an amount beyond about 5 parts by weight can make the resulting composition difficult to granulate, thereby hampering stable production. A preferred range is between about 0.05 and about 1 part by weight and a more preferred range is between about 0.1 and about 0.5 part by weight. In this range the balance between flame retardance, moldability, and impact strength is further improved.
The polycarbonate resin (A) may be mixed, unless the addition does not impair the advantageous effects of the invention, with other additives, such as any of various heat stabilizers, antioxidants, colorants, fluorescent brighteners, fillers, mold releasing agents, softening agents, antistatic agents, impact property improvers, and other polymers.
Heat stabilizers are, for example, metal hydrogensulfates such as sodium hydrogensulfate, potassium hydrogensulfate, and lithium hydrogensulfate, and metal sulfates such as aluminum sulfate. Such a stabilizer is usually used in an amount of from about 0 to about 0.5 part by weight per 100 parts by weight of a polycarbonate resin (A).
Fillers include glass fiber, glass beads, glass flakes, carbon fiber, talc powder, clay powder, mica, potassium titanate whiskers, wollastonite powder, and silica powder.
Among impact property improvers are acrylic elastomers, polyester elastomers, core-shell type methyl methacrylate-butadiene-styrene copolymer, methyl methacrylate-acrylonitrile-styrene copolymer, ethylene-propylene rubber, and ethylene-propylene-diene rubber.
Examples of other polymers are polyesters, such as polyethylene terephthalate and polybutylene terephthalate; polystyrenes; styrenic polymers, such as high-impact polystyrenes, acrylonitrile-styrene copolymer and its acrylic rubber modification products, acrylonitrile-butadiene-styrene copolymer, and acrylonitrile-ethylene-propylene-diene rubber (EPDM)-styrene copolymer; polypropylenes; and polymers usually used as alloyed with polycarbonate resins.
There is no special limitation to the method of mixing the various components in the flame-retardant polycarbonate resin composition of the invention. For example, either mixing by means of a conventional mixer such as a tumbler, a ribbon blender or melt mixing by an extruder may be used.
As for the method of molding the flame-retardant polycarbonate resin composition of the invention, injection molding, injection-compression molding, or other conventional molding technique can be employed without special limitation.